The left hemisphere activation hypothesis proposes that criminal psychopaths are characterized by inefficient cognition under conditions that activate left hemisphere-specific processing resources. This hypothesis appears consistent with several recent studies of psychopaths' language processing and divided attention performance. It also has novel applications for explaining and treating psychopaths' impulsive antisocial behavior. The current proposal is designed to examine whether the left hemisphere activation hypothesis can account for criminal psychopaths' documented deficits in selective attention and emotional processing. Based on evidence that left hemisphere resources mediate processing of local stimulus features, language stimuli, and states of appetitive motivation, left hemisphere activation inductions have been developed that make it possible to evaluate the adequacy of the left hemisphere activation hypothesis relative to other promising hypothesis for psychopaths' performance deficits. Findings consistent with the left hemisphere activation hypothesis will warrant reinterpretation of several of psychopaths' deficits in attention and emotional processing as apparent consequence of a single underlying dysfunction associated with the dynamic process of activation of left hemisphere processing resources. Two studies also attempt to replicate previous left hemisphere activation deficits with additional controls to rule out methodological explanations of these findings. Supplementary goals include examination of the specific dimensions of psychopathy that predict information-processing deficits, of the generality of these deficits across race and gender, and analysis of the independence/relatedness of cognitive deficits observed in distinct domains.